Method and device for regulating temperature of pressing sleeve

Abstract

The invention relates to a method for regulating the temperature of a press sleeve (6) provided with a recess on the outer side in a press assembly in order to increase the dry weight content of a fibrous web, comprising the following steps in the intended use of the press sleeve (6): a) determining the current actual temperature of the press sleeve (6); b) determining a current target temperature of the pressing sleeve (6); and c) if there is a deviation between the current actual temperature and the current target temperature, heating or cooling the pressing sleeve (6) so that the current actual temperature changes in the direction of the current target temperature; wherein the current target temperature is continuously reduced as the time of use of the pressing sleeve (6) elapses. The invention further relates to a press assembly for carrying out the method according to the invention and to a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, comprising such a press assembly.

Description

Technical Field

[0001] This invention relates to a method for temperature regulation of a press sleeve with a recessed portion on its outer side in a press assembly to increase the dry weight content of the fiber web. The method includes the following steps during the prescribed use of the press sleeve: a) Determine the current actual temperature of the press sleeve; b) Determine the current target temperature of the press jacket; c) When there is a deviation between the current actual temperature and the current target temperature, the pressing sleeve is heated or cooled to make the current actual temperature change in the direction of the current target temperature.

[0002] Furthermore, the present invention also relates to a pressing assembly for performing a temperature regulation method and a machine for manufacturing fiber webs, particularly paper webs, paperboard webs or cotton webs, the machine including such a pressing assembly. Background Technology

[0003] Machines used for manufacturing fiber webs (e.g., paper webs, paperboard webs, or cotton webs) typically have a press assembly in which the fiber web is dehydrated or dehumidified by mechanical pressure, thereby increasing the dry weight content of the fiber web. The press assembly is often arranged between the forming section and the drying section. Such a press assembly generally has at least one press sleeve, wherein the term "press sleeve" should be interpreted broadly for the purposes of this invention. The press sleeve can refer both to the roll skin fixedly connected to the roll and to a flexible sleeve, such as the flexible sleeve required for a press assembly with an extended press gap. In particular, the latter is of interest to this invention because press assemblies with extended press gaps offer several advantages: the press gap is planar, unlike the essentially linear shape of a conventional roll press. As a result, the pressure applied to the fiber web to be dehydrated along the running direction in the press gap does not build up abruptly, but rather increases continuously from a low value to a high value. This reduces the risk of the fiber web to be dehydrated being crushed in the press gap. Furthermore, the residence time within the press gap is extended. This allows the fiber web to be dehydrated very efficiently without compromising volume within the extended press gap. For example, the fiber web can be guided through the extended press gap together with felt or between two felts, where, in a so-called shoe press, the extended press gap can be formed between the shoe press roll and the mating roll. Water squeezed out from the fiber web and its conveying felt in the pressing zone can be temporarily contained via a recess on the outer side of the press sleeve.

[0004] Methods for temperature regulation of the press sleeve are known in the prior art. For example, document DE 37 05 241A1 proposes that, in the pressing zone of an extended pressing gap in a shoe press, different pressures and temperatures are selectively adjusted in sections along the fiber web's travel direction. This is achieved through a pressure medium between the press shoe and the press sleeve, wherein the pressure medium is correspondingly temperature-adjusted to heat or cool the press sleeve. By simultaneously applying pressure and heat in the pressing gap, increased dehydration can be achieved without the risk of damaging the fiber web.

[0005] Furthermore, document WO 93 / 23614 A1 proposes a shoe-type pressing assembly in which temperature sensors are installed at both the leading and trailing edges of the pressing shoe. If a temperature difference is detected, the leading and / or trailing edges are selectively cooled or heated using a temperature-controlled fluid to achieve temperature equilibrium. This helps to suppress undesirable deformation of the pressing shoe during operation. However, during intended operation, the pressing shoe presses against the pressing sleeve, thus the temperature of the pressing shoe also affects the temperature of the pressing sleeve.

[0006] A known drawback of existing pressing components is that (regardless of temperature control) the dehydration capacity of the pressing sleeve generally deteriorates significantly over time. This is primarily due to the wear and tear that occurs over time as the pressing sleeve bears the heavy loads it is expected to operate under. This causes the depth of the recesses (such as dehydration grooves) to decrease, and consequently, the amount of water these recesses can hold. This phenomenon is known as a reduction in the "void volume" of the pressing sleeve. This process is analogous to the wear and tear on a car tire tread over time. If the wear becomes excessive, the worn-out pressing sleeve must be replaced with a new one. Summary of the Invention

[0007] The objective of this invention is to solve or at least mitigate the aforementioned problems. In particular, it is necessary to suppress the problem that the dehydration capacity of the press sleeve deteriorates over the course of its service life.

[0008] This task is solved by the features of the independent claim. The dependent claims are the subject of advantageous improvements to the invention. Therefore, this task is solved by the aforementioned method for temperature regulation of the press sleeve, characterized in that the current target temperature is continuously reduced as the press sleeve is used. The inventors have recognized that temperature has a significant effect on the material strength or modulus of elasticity of the press sleeve. Generally, the strength or shape stability of a material is higher at lower temperatures than at higher temperatures. The inventors have also recognized that this fact can be specifically utilized to suppress the reduction in void volume of the press sleeve due to wear over time. In this way, the dehydration performance can be maintained at an acceptable level for a longer period.

[0009] It is crucial to understand that for the pressing assembly to achieve optimal dewatering performance, the pressing sleeve must possess a precisely defined void volume. If the void volume is too small, oversaturation may occur in the pressing gap, leading to undesirable backsplashing of water against the machine's direction of rotation (also known as "backsplashing"), or similarly undesirable high hydraulic pressure in the recesses of the pressing sleeve. Conversely, if the void volume is too large, undersaturation occurs in the pressing gap, resulting in deteriorated dewatering performance. Both excessively small and excessively large void volumes result in lower dry weight content of the fiber web following the pressing assembly, or in other words, reduced machine "runability." The optimal void volume depends primarily on the basis weight and dry weight content of the fiber web preceding the pressing assembly. Typically, new rollers are selected such that their void volume is adapted to the characteristics of the aforementioned fiber web. It has been taken into consideration that the void volume decreases due to the pressure established in the pressing gap. The reason is that the material of the press sleeve is compressed in the press gap and partially retreats into the void volume.

[0010] According to the present invention, if the temperature of the pressing sleeve is continuously reduced over time, the strength or shape stability of the pressing sleeve material will continuously increase. Consequently, under the same pressure in the pressing gap, the material deformation continuously decreases, and thus the reduction in void volume also continuously decreases. Therefore, void volume reduction caused by pressing sleeve wear can be suppressed, and the optimal dewatering capacity of the pressing sleeve can be maintained for a longer period.

[0011] As is commonly used, especially in the roller sleeves of boot presses, the recess can also be constructed in the layer of the press sleeve that contains polyurethane, preferably entirely composed of polyurethane.

[0012] Polyurethane is a type of material that is not only easy to process for this purpose, but also has the characteristic that its strength or shape stability is largely dependent on temperature.

[0013] In particular, polyurethane can be formed by reacting a prepolymer with a crosslinking agent component, wherein the prepolymer is a reaction product of 4,4'-diphenylmethane diisocyanate (MDI) and a polyol component containing at least one polycarbonate polyol, and wherein the crosslinking agent component contains a diol. In particular, the crosslinking agent component may contain butanediol (BDO). This type of polyurethane has proven particularly suitable for temperature control according to the invention because temperature has been found to have a particularly significant effect on the dynamic compressive modulus.

[0014] As mentioned above, the press sleeve used in this invention preferably relates to a boot-type press sleeve. This press sleeve (especially when it is a boot-type press sleeve) should be constructed to be impermeable to prevent leakage and potential contamination of the fiber web by the lubricating oil used to guide lubrication between the press shoe and the press sleeve. Additionally, the recesses preferably have the shape of at least one continuous or discontinuous groove, wherein the one or more grooves preferably extend helically substantially in the circumferential direction of the press sleeve. This design has proven effective in practice on numerous occasions and is relatively simple to manufacture.

[0015] A simple and therefore preferred variation of determining the current actual temperature in step a) is proposed, preferably by measuring the current actual temperature directly on the outside of the press sleeve in a non-contact manner. For this, a thermometer that functions non-contactly via infrared light or visible laser light can be used, for example. The use of a thermal imaging camera is also feasible.

[0016] An alternative variation for determining the current actual temperature in step a) is proposed, which utilizes a temperature sensor integrated into the press sleeve. In a typical boot-type press sleeve, there is generally a reinforcing structure made of yarn layers or yarn fabric embedded and encased within a matrix structure, particularly made of polyurethane. Recently, the apparel industry (especially in functional clothing) has introduced specially developed sensors with yarn-like structures, which can then be integrated into the fabric of textiles. Simultaneously, data detected by the sensors can be read via RFID technology and transmitted, for example, to nearby mobile terminal devices. These yarn-like sensors, developed for the textile industry and employing RFID technology, can also be excellently integrated into the reinforcing structure of the press sleeve without causing problems as interference.

[0017] Although wear caused by operating time and the associated reduction in void volume have the greatest impact on the dehydration capacity of the press jacket over time, other influencing parameters also change within a certain range over time (assuming other machine settings are the same). Therefore, in an advantageous improvement of the invention, it is proposed that, in step b), when determining the current target temperature, at least one (preferably more) of the following influencing parameters be considered: i) Dry weight content of the fiber web before the pressing unit; ii) Gram weight of fiber width; iii) The operating time of the pressing sleeve; iv) Wear condition of the press sleeve; v) Machine speed; vi) The pressure profile and / or peak pressure in the pressing zone formed by the fiber width during the specified operation of the press sleeve; vii) The operating time and / or volume of the felt arranged between the press sleeve and the fiber web during the specified operation of the press sleeve.

[0018] These relationships can be quite complex and not fully known; therefore, it is proposed that, in step b), a self-learning adjustment algorithm be employed when determining the current target temperature. Today, even in highly complex situations, the optimal adjustment target value can be determined relatively simply and quickly with the help of artificial intelligence.

[0019] In step c), to ensure that the current actual temperature matches the current target temperature, several alternative or cumulative feasible solutions exist. One feasible solution proposes applying (especially spraying) a coolant (preferably cooling water) to the outside of the pressing sleeve. Another feasible solution proposes embedding temperature-regulating elements in the material of the pressing sleeve itself. These temperature-regulating elements can be either heated or cooled by an electric current. The current can be introduced inductively. Furthermore, yet another feasible solution proposes adjusting the temperature and / or flow rate of the circulating fluid (especially cooling oil) inside the pressing sleeve. This is essentially equivalent to the solutions described in the aforementioned prior art, namely DE 37 05 241 A1 and WO 93 / 23614 A1, the relevant disclosures of which are cited herein.

[0020] According to another aspect of the invention, the aforementioned task is also solved by a pressing assembly for increasing the dry weight content of the fiber web, the pressing assembly comprising a pressing sleeve with a recessed portion on its outer side and a mechanism for temperature regulation of the pressing sleeve, preferably according to the aforementioned method according to the invention, wherein the temperature regulation mechanism comprises: a) A mechanism for determining the current actual temperature of the press sleeve; b) A mechanism for determining the current target temperature of the press jacket; c) A mechanism for heating or cooling the press jacket, thereby causing the current actual temperature to change in the direction of the current target temperature when there is a deviation between the current actual temperature and the current target temperature; The mechanism for determining the current target temperature is configured to continuously decrease the current target temperature as the pressing sleeve is used.

[0021] The advantages and technical effects described above with respect to the method according to the invention are equally applicable to the pressing assembly according to the invention, and vice versa.

[0022] The pressing assembly may also include a matching roller to form a pressing gap for the fiber web together with the pressing sleeve.

[0023] In addition, the present invention relates to a machine for manufacturing fiber webs (especially paper webs, paperboard webs or cotton webs), the machine comprising the pressing assembly described above according to the present invention. Attached Figure Description

[0024] The present invention will now be described in detail with reference to the embodiments illustrated in the accompanying drawings. In the drawings: Figure 1 A schematic diagram of a pressing assembly 1 with a pressing sleeve 6 is shown. Figure 2 It shows Figure 1 A schematic cross-sectional view of a section of the pressing sleeve 6; Figure 3 This diagram illustrates the active temperature control of the pressing sleeve 6. Figure 4 A schematic diagram illustrating the effect of temperature on the dynamic compressive modulus of the material in the press sleeve 6 as a function of load rate is shown; and Figure 5 This diagram illustrates the effect of temperature on the reduction of the void volume in the press sleeve 6 as pressure changes. Detailed Implementation

[0025] Figure 1A schematic diagram of the pressing assembly 1 is shown, wherein, in this embodiment, the pressing assembly is configured as having an extended pressing gap 7. Such a pressing assembly 1 is also referred to as a shoe press. The extended pressing gap 7 is provided by two pressing elements, namely, by a shoe press roll 2 and a mating roll 3. The shoe press roll 2 includes a pressing shoe 5 supported on a vertical yoke 4 and a flexible pressing sleeve 6 arranged in a manner rotatable about the pressing shoe 5. During the prescribed operation of the pressing assembly 1, the fiber web 8 to be dewatered is preferably guided in a sandwich-like manner between two pressing felts 9 through the extended pressing gap 7. The pressing shoe 5 has a substantially concave surface through which the pressing sleeve 6 operates, while the pressing shoe 5 presses the pressing sleeve towards the mating roll 3 with a high pressure F.

[0026] The pressure F that causes the press shoe 5 to press against the press sleeve 6 is preferably selected to be sufficient to make the peak pressure acting on the fiber web 8 in the extended press gap 7 at least 8 MPa, preferably at least 10 MPa. The length of the extended press gap of the main press 1 is preferably at least 150 mm, more preferably at least 190 mm.

[0027] At such peak pressures, it has proven particularly advantageous that the boot press sleeve 6 is at least partially composed of polyurethane formed by reacting a prepolymer with a crosslinking agent component, wherein the prepolymer is a reaction product of 4,4'-diphenylmethane diisocyanate (MDI) and a polyol component containing at least one polycarbonate polyol, and wherein the crosslinking agent component contains a diol, particularly butanediol (BDO).

[0028] like Figure 2 As schematically shown in an enlarged cross-sectional view of the press sleeve 6, a reinforcing structure 11 in the form of a yarn lay-up or yarn fabric can be embedded in the polyurethane. Furthermore, the press sleeve 6 has recesses 10 on its outer side, which can be configured as multiple grooves extending spirally in the circumferential direction of the press sleeve 6. These recesses are used to provide a so-called void volume for the liquid to accommodate the liquid from the fiber web 8 or the press felt 9 arranged between the fiber web 8 and the press sleeve 6 in the extended press gap. In this embodiment, according to... Figure 2 In the view, at least when the press sleeve 6 is still in a brand new condition and unloaded, the recess is substantially rectangular in structure, with a defined width and a defined height. If the press sleeve 6 is subjected to pressure F in the extended press gap 7, the polyurethane of the press sleeve 6 will elastically and partially press into the gap volume, thereby reducing the gap volume, especially in its extension along the width direction. Furthermore, as the press sleeve 7 is used over time, the polyurethane is continuously worn away, thereby continuously reducing the gap volume, especially in its extension along the height direction.

[0029] Although the first effect (i.e., the reduction in void volume due to the pressure F in the extended pressing gap 7) is generally taken into account in the design of the pressing sleeve 6 during its installation, so that the pressing sleeve can initially operate within the optimal saturation range, the second effect, namely the reduction in void volume due to wear of the pressing sleeve 6 over time, has not yet been specifically suppressed. This invention is based on this point.

[0030] While this invention cannot prevent wear of the press sleeve 7 over time, the inventors have found another way to suppress the resulting reduction in void volume. Therefore, the inventors discovered that the void volume loss due to material compression in the press gap is directly related to the dynamic compressive stiffness of the press sleeve material. Further research shows that, depending on the material, the stiffness of the press sleeve 7 changes significantly with temperature. This invention utilizes this effect by integrating active temperature control of the press sleeve 7 into the control of the press assembly 1.

[0031] For example, such as Figure 3 As schematically shown, such active temperature regulation can be configured. Here, the current actual temperature of the pressing sleeve 6 is measured via temperature sensor 12. For example, this measurement can be performed non-contactly from the outside of the outer surface of the pressing sleeve 6, or the temperature sensor 12 can be embedded in the polyurethane of the pressing sleeve 6. The measured current actual temperature is transmitted by the temperature sensor 12 to the temperature regulation unit 13 via a wired or wireless signal line. The temperature regulation unit 13 compares the current actual temperature with the current target temperature, and if there is a deviation between the current actual temperature and the current target temperature, heats or cools the pressing sleeve 6, thereby changing the current actual temperature toward the current target temperature. The temperature regulation unit 13 can trigger this, for example, by manipulating the internal temperature regulating element 14 (especially the temperature regulating element 14 embedded in the polyurethane of the pressing sleeve 6). Alternatively or additionally, the temperature regulation unit 13 can also manipulate the pressing sleeve cooling pump 15 and / or the cooling oil pump 16. The press jacket cooling pump 15 can apply coolant (especially water) to the outside of the press jacket 6 via an external temperature control element 17 (e.g., a nozzle) to specifically cool the press jacket. Meanwhile, the cooling oil pump 16 can pump cooling oil 18 into the interior of the boot press roll 2, where the cooling oil can specifically cool the press jacket 6 from the inside, for example, within the area of ​​the extended press gap 7.

[0032] It should be noted that, as is the case with such pressing assemblies, in addition to the cooling oil 18, other oil flows can be pumped into the interior of the shoe press roll 2, for example, oil 20 for lubricating and / or cooling the press shoe 5 and / or oil 21 for controlling the pressing force of the press shoe 5, pumped in particular by means of the pressure oil pump 19. The oils 18, 20, 21 introduced into the interior of the shoe press roll 2 can be returned to the cooling oil pump 16 and / or the pressure oil pump 19 via return lines, wherein a heat exchanger 22 is preferably provided in the return section to cool the oil, for example, by means of cooling water.

[0033] The dynamic compression modulus can be affected by the temperature of the pressing sleeve 6 through the active temperature regulation of the temperature regulation unit 13, and thus the void volume. Figure 4 The figure illustrates how the dynamic compressive modulus (in MPa) plotted on the Y-axis varies with the loading rate (in MPa / s) plotted on the X-axis, depending on temperature, for a specific polyurethane (referred to herein as PU-A). As shown, at both 25°C and 60°C, the dynamic compressive modulus increases with increasing loading rate, but the curve at 25°C is generally higher than that at 60°C. In other words, at lower temperatures, the polyurethane exhibits a higher dynamic compressive modulus, meaning better shape stability.

[0034] According to the present invention, if the current target temperature is continuously reduced as the pressing sleeve 6 is used, the material of the pressing sleeve 6 will always maintain better shape stability. In this way, the reduction in void volume due to elastic deformation of the pressing sleeve 6 in the extended pressing gap 7 is continuously reduced. Therefore, the reduction in void volume due to wear of the pressing sleeve 6 over time can be suppressed. Thus, the void volume is maintained within the range of optimal dewatering capacity of the pressing sleeve for a longer period, or the rate at which it falls out of this range is significantly slowed. This is achieved in… Figure 5 The diagram illustrates the percentage decrease in void volume as a function of pressure (in MPa) on the Y-axis. It is clear from the figure that the curve at only 20°C extends much more gently than the curve at 60°C.

[0035] Finally, it should be noted that in practice, the void volume not only decreases over time due to wear of the press sleeve 6, but the material of the press sleeve 6 (especially when it is mainly made of polyurethane) also loses strength over time due to hydrolysis, thus becoming unable to withstand the pressure in the extended press gap 7. This causes the material to elastically deform towards the recess 10, which in turn leads to a reduction in the void volume in the extended press gap 7. According to the present invention, this effect can also be suppressed by actively regulating the temperature of the press sleeve 6.

[0036] List of reference numerals

[0037] 1. Pressing Components

[0038] 2 Shoe-type press rolls

[0039] 3. Matching rollers

[0040] 4. Vertical yoke

[0041] 5. Press Boots

[0042] 6 Pressing sleeve

[0043] 7. Extended pressing interval

[0044] 8. Fiber width

[0045] 9 Press Felt

[0046] 10. Depression

[0047] 11. Strengthen the structure

[0048] 12 Temperature Sensors

[0049] 13 Temperature control unit

[0050] 14. Internal temperature control element

[0051] 15 Press jacket cooling pump

[0052] 16 Cooling oil pump

[0053] 17. External temperature control element

[0054] 18 Cooling oil

[0055] 19. Pressure oil pump

[0056] 20 Oil for lubricating and / or cooling the press boot 5

[0057] 21. Oil used to control the pressing force of the press shoe 5

[0058] 22 Heat Exchanger

[0059] F pressure

Claims

1. A method for temperature regulation of a press sleeve (6) having a recess (10) on its outer side in a press assembly (1) to increase the dry weight content of the fiber width (8), the method comprising the following steps in the prescribed use of the press sleeve (6): a) Determine the current actual temperature of the press sleeve (6); b) Determine the current target temperature of the press sleeve (6); c) If there is a deviation between the current actual temperature and the current target temperature, the pressing sleeve (6) is heated or cooled so that the current actual temperature changes in the direction of the current target temperature; The feature is that the current target temperature decreases continuously as the pressing sleeve (6) is used for a period of time.

2. The method according to claim 1, Its features are, The recess (10) is constructed in a polyurethane-containing, preferably entirely polyurethane-based layer of the press sleeve (6).

3. The method according to claim 2, Its features are, The polyurethane is formed by reacting a prepolymer with a crosslinking agent component, wherein the prepolymer is a reaction product of 4,4'-diphenylmethane diisocyanate (MDI) and a polyol component containing at least one polycarbonate polyol, and wherein the crosslinking agent component contains a diol.

4. The method according to claim 3, Its features are, The crosslinking agent component includes butanediol (BDO).

5. The method according to any one of the preceding claims, Its features are, At least one of the following statements is true: i) The pressing sleeve (6) is a boot-type pressing sleeve; ii) The pressing sleeve (6) is constructed to be impermeable; iii) The recess (10) has the shape of at least one continuous or discontinuous groove, wherein one or more grooves preferably extend in a spiral shape substantially in the circumferential direction of the press sleeve (6).

6. The method according to any one of the preceding claims, Its features are, In step a), the current actual temperature is preferably measured directly on the outside of the press sleeve in a non-contact manner.

7. The method according to any one of the preceding claims, Its features are, In step a), the current actual temperature is measured using a temperature sensor integrated into the pressing sleeve.

8. The method according to any one of the preceding claims, Its features are, In step b), when determining the current target temperature, at least one, preferably multiple, of the following influencing parameters are considered: i) The dry weight content of the fiber web (8) prior to the pressing assembly (1); ii) The basis weight of the fiber width (8); iii) The operating time of the pressing sleeve (6); iv) The wear condition of the press sleeve (6); v) Machine speed; vi) The pressure profile and / or peak pressure in the pressing zone (7) formed by the fiber web (8) during the prescribed operation of the press sleeve (6); vii) The operating time and / or volume of the felt (9) arranged between the press sleeve (6) and the fiber web (8) during the specified operation of the press sleeve (6).

9. The method according to any one of the preceding claims, Its characteristic is that, in step b), a self-learning adjustment algorithm is used to determine the current target temperature.

10. The method according to any one of the preceding claims, Its features are, In step c), in order to make the current actual temperature consistent with the current target temperature, coolant, preferably cooling water, is applied, especially sprayed onto the outside of the press sleeve (6).

11. The method according to any one of the preceding claims, Its features are, In step c), a temperature regulating element is embedded in the material of the pressing sleeve itself in order to make the current actual temperature consistent with the current target temperature.

12. The method according to any one of the preceding claims, Its features are, In step c), in order to make the current actual temperature consistent with the current target temperature, the temperature and / or flow rate of the circulating fluid, especially the cooling oil (18), are adjusted inside the press sleeve.

13. A pressing assembly (1) for increasing the dry weight content of a fiber width (8), the pressing assembly comprising a pressing sleeve (6) having a recess (8) on its outer side and a mechanism for temperature regulation of the pressing sleeve (6), preferably temperature regulation according to at least one of the preceding claims, wherein, Mechanisms used for temperature regulation include: a) A mechanism (12) for determining the current actual temperature of the press sleeve (6); b) A mechanism for determining the current target temperature of the press sleeve (6); c) Mechanisms (14, 15, 16, 17) for heating or cooling the pressing sleeve (16), thereby causing the current actual temperature to change in the direction of the current target temperature when there is a deviation between the current actual temperature and the current target temperature; The feature is that the mechanism for determining the current target temperature is configured to continuously reduce the current target temperature as the pressing sleeve (6) is used for a period of time.

14. The pressing assembly (1) according to claim 13. Its features are, The pressing assembly (1) also includes a matching roller (3) to form a pressing gap (7) for the fiber web (8) together with the pressing sleeve (6).

15. A machine for manufacturing fiber webs (8), particularly paper webs, paperboard webs or cotton webs, said machine comprising a press assembly (1) according to claim 13 or 14.

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